Quote Karl H.:
As far as I have understood things, PCIX was a pretty straight-forward extension of PCI (possibility of 64-bits wide rather than 32 bit, doubled clock rate from 33 MHz to 66 MHz).
However, it looks like this was too small a step for most industry players, so PCIe appeared, which is a serial bus (unlike PCI and PCIX). Instead of having 32 or 64 parallel lines at relatively low clock rates, they choose to go with serial (1 bit wide) at much higher clock rate. This is a general trend in the industry, same thing with SATA, for example.
PCIe x1 means just one serial channel, while PICe x16 has 16 serial channels, and should therefore have 16 times the throughput. The reason this still works better than parallel is that in 16x, each serial channel has its own clock, so skew is not a problem like it was in the parallel configuration (when all the data lines shared a single clock).
So, the PCIE x 16 and a PCIX slot are definitely 2 different things. I can see the PCIe x 1 looks radically different - it is a very small connector. But the PCIe x 16 looks like an ordinary PCI slot, which in turn looks like PCIX.
Am I right in thinking that an ordinary PCI card will fit in a PCIE x 16 slot?